1. Field
The present invention relates generally to wireless telephone communications, and specifically to measurement of received signal strength.
2. Background
One of the parameters that is important to determine for efficient operation of a base-station transceiver system (BTS) in a cellular telephone network is the reverse link excess capacity of the BTS. The reverse link excess capacity is measured in terms of a theoretical maximum number of users of the BTS, which in turn is a function of the energy received by the receiving system of the BTS compared with a noise figure of the receiving system. Accurate measurement of this energy difference is difficult to perform.
Methods are known in the cellular network art for determining the noise figure of the receiving system, which is a function of the inherent thermal noise as well as a noise contribution from the receiving system itself. The noise contribution from the receiving system is based on the inherent thermal noise and the gain (or loss) of the elements in the receiving system. For example, the noise contribution of each of the elements in the receiving system at the BTS, from the antenna to the final detector of the system, may be evaluated, and combined with the inherent thermal noise. However, while determination of noise contributions and gain of passive components in the receiving system is relatively straightforward, and the values do not change over time, this is typically not the case for active components. Determination of the noise contribution and gain from active components is usually more complicated and time-consuming; in addition, the noise contribution of active components typically changes over time, and such change may be difficult to predict. Furthermore, and adding to the complication, the noise figure of the receiving system is typically frequency and part dependent, as well as varying with temperature.
Measurement of the energy received by the receiving system at the detector typically suffers from the same problems mentioned above, namely, gain variation with temperature, frequency, and time.
An alternative method for measuring the relative noise level of the receiving system, known in the art, is to arrange that all mobile transceivers transmitting to a BTS are simultaneously silent for a short time period, during which the noise at the BTS may be measured. This method has the advantage, compared to the method described above, of being operable in an active system, at the cost of a reduction of resources during the silent period and the complexity of reacquiring the mobile transceiver signals. In addition, the method suffers from the fact that the BTS can only silence mobile transceivers it controls, and cannot prevent other transmissions from reaching the BTS, unless all BTSs are synchronized and perform the silencing at the same time.
There is thus a need for an improved method for measuring the noise figure of a receiving system in a BTS, for the purposes of measuring the reverse link excess capacity of the BTS.